The present invention relates to improvements in automotive temperature control systems for controlling the temperature in the vehicle passenger compartment. Systems of this type usually employ an air blend door for mixing blower driven heated air from the passenger compartment heater with cooled air from the vehicle air conditioning system in the proper proportions to maintain the passenger compartment at a desired temperature. In such systems the air blend door is typically disposed in ducting supplied by a blower and the blend door is typically operated by a servoactuator powered by a fluid pressure control signal. The control signal is typically generated by a modulator valve, supplied by a source of vacuum on-board the vehicle, and the modulator valve is operated by a temperature sensor which senses the temperature of a flow of air from the vehicle passenger compartment. A control usually located in the vehicle passenger compartment, upon selective positioning, biases the temperature sensor a predetermined amount such that the sensor alters the position of the modulator valve thereby creating a vacuum signal to the actuator and moving the air blend door to increase the amount of heating or coolng of the passenger compartment until the predetermined input to the sensor is neutralized by a corresponding change in the sensed temperature of a flow of passenger compartment air.
Examples of systems operating in this general manner are described in my earlier U.S. Pat. Nos. 3,770,195, 3,774,696, 3,838,841 and 3,983,930; all of which employ regulators utilizing a bimetal actuated temperature sensormodulator valve combination located remotely from the servoactuator for moving the air blend door.
Automatic temperature control systems for the passenger compartment may be arranged to function in any of several desired ways, the most common being of two types, one utilizing the air blend door to mix separate streams of blown air from the air conditioning cooler, or evaporator, and air heated from passage over a heater core operating from engine coolant and in such an arrangement the cooling system or the heater may be operated independently of each other. The second type system requires that the air conditioning system be in operation at all times when the ambient air external to the passenger compartment is above 40.degree. F., whereupon all incoming air to the blower system is first cooled by passage over the air conditioner evaporator and dehumidified; and, the blend door is used to control the amount of cooled dehumidified air which is passed over the heater core and heated before discharge into the passenger compartment.
In the prior automatic temperature control systems utilizing a bimetal temperature sensing element, the bimetal element has been located in an aspirator inlet flow passage, the aspirator receiving ambient air through a nozzle from a blower, which nozzle entrains a flow of in-car air through the aspirator inlet, which entrained flow passes over the bimetal sensing element. This arrangement has necessitated the location of the sensing bimetal some distance from the modulator valve in order to position the bimetal within the aspirator inlet. The remote location of the sensing bimetal from the modulator valve has required intermediate connecting members to transmit the temperature change-induced motion of the bimetal element to the modulator valve. In such prior systems a mechanism has been provided for biasing the bimetal by a predetermined amount by selective movement of the operator's control in the passenger compartment. This arrangement has required that the preload mechanism be associated with the connecting linkages between the bimetal and modulator valve.
In order to calibrate systems arranged in the above-described manner, it has been necessary to assemble the modulator valve, the interconnecting linkages, the sensing bimetal and preload mechanism within the aspirator prior to affecting calibration of the modulator valve-sensor combination, sometimes referred to together as a "sensor." The intermediate linkages employed to transmit motion of the bimetal temperature sensing element to the modulator valve have rendered the assembly and calibration of the sensor combination as costly and difficult procedures during manufacture.
Furthermore, it has long been desirable in designing automotive automatic temperature control systems to provide feedback of the blend door actuator position to the sensor in order to attenuate the effect of large control signal inputs from the operator selective control where a great difference exists between the in-car temperature and the ambient temperature external to the vehicle passenger compartment. Previous systems of the type using a force balance equilibrium between the modulator valve and the temperature sensing element, when the in-car temperature was at the desired level, have not incorporated feedback from the actuator output to the temperature sensor. This has been chiefly due to the remote location of the sensor from the output actuator and, thus, direct mechanical feedback has been virtually impossible.